The rise of Internet usage in recent years, etc. have brought increasing desire of data communication, typically through IP (Internet Protocol), in the SONET/SDH networks originally designed to carry voice traffic. However, because of the SONET/SDH standards designed for application to voice traffic, there has been a problem of inefficiency in data communication from the viewpoint of network bandwidth usage.
As techniques for solving such a problem, Virtual Concatenation (hereafter referred to as VCAT) and Link Capacity Adjustment Scheme (hereafter referred to as LCAS) have been devised.
FIG. 1 is an exemplary configuration of transmission equipment using VCAT and LCAS. In this transmission equipment, packets input from a plurality of ports P1, P2 via Ethernet interfaces 4, 5 (‘Ethernet’ is a trademark) are forwarded to a VCAT controller 2. In this VCAT controller 2, a plurality of VCAT member paths having a common destination are collected into a VCAT path.
After switched to a corresponding route by a switch SW, the VCAT path is forwarded to an OC-n line 100 connected to a SONET/SDH network 101, via an OC-n interface 1.
Here, when accommodating a 100-Mbps Fast Ethernet packet input to SONET/SDH network 101 at a maximum rate, two STS 1 paths (51.84 Mbps each) bundled into an STS 1-2v path (approximately 100 Mbps) can be used.
Without use of such VCAT, it is compelled to use an STS-3c path (approximately 155 Mbps) nearest to 100 Mbps, which results in wasting 55 Mbps.
Further, in LCAS (Link Capacity Adjustment Scheme), addition or deletion of SONET/SDH unit paths (VCAT member paths) in a VCAT bandwidth can be performed without interrupting the transmission service, by use of LCAS controller 3. Also, in the event of failure on a VCAT path, the transmission service can be continued by automatically deleting the failed path from VCAT.
As a technique for changing a VCAT bandwidth (the number of VCAT member paths) without interrupting the transmission service, LCAS has been standardized in ITU-T Recommendation G.7042/Y.1305, Link Capacity Adjustment Scheme (LCAS) for Virtual Concatenated Signals, November, 2001.
When increasing the VCAT bandwidth, namely when adding a VCAT member path, an ADD command (refer to FIG. 7) is described in the H4 byte of POH (path overhead) of the VCAT member path concerned, thereby enabling synchronization of bandwidth change timing on both the transmitting side and the receiving side. With this, uninterrupted bandwidth change can be attained.
Similarly, when decreasing the VCAT bandwidth, namely when deleting a VCAT member path, an IDLE command (refer to FIG. 7) is described in the H4 byte of POH of the VCAT member path concerned, thereby enabling synchronization of a bandwidth change timing on the transmitting side and the receiving side. With this, uninterrupted bandwidth change is also attained.
When the bandwidth is to change without use of LCAS, it is necessary to disconnect the VCAT once. Also, data transmission becomes disabled when a failure occurs in any one path of the VCAT member paths. Therefore, by introducing VCAT and LCAS, efficient usage of the bandwidths in SONET/SDH network 101 can be attained even when the network is used for data communication.
Additionally, as a related known art, there has been a technique such as shown in the official gazette of the Japanese Unexamined Patent Publication No. 2002-368774.
Namely, in order to improve network use efficiency of the network shown in FIG. 1, in a communication apparatus transmitting data from a LAN to a SONET network, buffer capacity of the mounted LAN interfaces 4, 5 is monitored. When the capacity exceeds a predetermined threshold, and when there is an idle line capacity left on the SONET side, the SONET network bandwidth in VCAT controller 2 is expanded and the concatenation setting of the SONET path transmitting the data from the LAN is changed.
More specifically, by monitoring both POH and LOP (Loss of Pointer), the communication apparatus on the opposite side also changes the concatenation setting of the SONET path, and completes the bandwidth change of the SONET path.
Here, transmission equipment is provided for transmitting input traffic to a remote place rapidly and securely. Missing input traffic is not desired. To prevent such a loss of input traffic, it is necessary to provide a bandwidth on the SONET/SDH network 101 side greater than bandwidths of input ports P1, P2.
However, the data communication traffic through IP, etc. being input to input ports P1, P2 has characteristics of intermittence, as well as abrupt increase or decrease of the data amount. Namely, in some cases there will be no data flow, while in other cases data will flow at a burst to the full bandwidth. Preferably, from the viewpoint of efficient network bandwidth usage, a necessary bandwidth is desirably allocated at necessary times. Also, when there is a room in the bandwidth, the remainder of the necessary bandwidth is to be used for other data transmission.
However, according to the technique disclosed in the aforementioned patent publication, although it is possible to change a path bandwidth on the SONET/SDH network side automatically, there is a problem of temporary interruption during the transmission service. By combining VCAT with LCAS, path bandwidth on the SONET/SDH network side can be changed without interruption. However, according to the conventional system configuration, this bandwidth change can only be performed by a command, issued from an externally provided network supervision and control system (hereafter referred to as network management system: NMS) 102 to a device monitoring and controlling section 6. With such a means, it is not possible to cope with abrupt change in the input traffic.
As a result, duration of no data transmission in a SONET/SDH path lasts for a certain period, which impedes efficient bandwidth use of the network. Or, flow control or data discarding may cause a problem of impeding the throughput in the upper layer.